We have been interested in the fundamental mechanisms that control cell proliferation, differentiation and death as related to cancer and AIDS, specifically in the biochemical networks regulating telomerase activity, BORIS expression and other cancer-related genes.Most human cancers express telomerase but its activity is highly variable and regulated by complex mechanisms. Recently, we have proposed that Ets proteins may be important for regulation of telomerase activity in leukemic cells. We provided further evidence for the role of Ets family members and related Id proteins in telomerase regulation, and characterize the underlying molecular mechanisms. By using a PCR-based and a gel shift assays we demonstrated specific binding to a core hTERT promoter of two Ets family members (Ets2 and Fli1), Id2, c-Myc, Mad1 and Sp1 in lysates from subclones of U937 cells. Further analysis of binding of purified proteins and various mutants of the hTERT promoter suggested the existence of a tri-molecular Ets-Id2-DNA complex, and Ets inhibitory activity mediated by c-Myc and the Ets binding site on the core hTERT promoter at -293 bp from the transcription initiation site as well as a positive Ets regulatory effect mediate through another Ets binding site at -36 bp. This analysis of the function of all Ets consensus binding sequences within the hTERT promoter provided evidence for the existence of negative and positive Ets regulatory sites and suggest a complex interplay between Ets/Id family members and c-Myc that may be an important determinant of the diversity of telomerase activity in leukemia and other cancers. We also studied the role of IL-2 in the dynamics of T cells in HIV infected patients. HIV infection leads to decreases in the number of CD4+ T lymphocytes and an increased risk for opportunistic infections and neoplasms. Intermittent IL-2 therapy can lead to substantial, sustained increases in CD4 cell numbers in HIV-infected patients. In vivo labeling with 2H-glucose and bromodeoxyuridine demonstrated that although therapy with IL-2 leads to high levels of proliferation of CD4+ as well as CD8+ lymphocytes, a preferential increase in survival of CD4+ cells (with half-lives that can exceed 4 years) is critical to the sustained expansion of these cells. Examination of lymphocyte subsets demonstrated that phenotypically nave (CD45RA+/CD27+) as well as central memory (CD45RA-/CD27+) CD4+ cells are preferentially expanded, suggesting that IL-2 can help maintain long-term memory to opportunistic pathogens.